BIOL 2306 – Living Planet (hybrid)
CONCEPTS FOR EPISODE 1
The populations of species that live and interact in a particular area comprise a community.
Each species interacts uniquely with both its biotic and abiotic environments, producing an
ecosystem. Populations, communities, and ecosystems change over time and space in a
variety of ways.
I.
Biological evolution occurs at the population level over many generations through
natural selection acting on individual organisms as they interact with their
environments with varying levels of success. (see Introduction outline, section III).
example: a mutation in a gene that influences tooth size in beavers arises in an individual,
giving it larger teeth. This gene is passed to its descendants, enabling them to chew down
trees more efficiently, build better dams and lodges and leave more offspring who
successfully rear more young who also inherit this gene, who rear more young, etc. etc..
Over time, less successful, smaller-toothed beavers will become increasingly scarce.
Eventually, over many generations, all beavers will have large teeth.
II.
Zonation results from the interaction among biotic and abiotic factors influencing
the types of organisms that can exist in a particular area. In general, the distribution
of plants depends on the distribution of abiotic factors (where tolerance levels are
met), and the distribution of animals depends on the distribution of the plants they
use for food or shelter.
examples: Mountains provide an opportunity to observe the results of these interactions as
communities change as physical factors change as altitude changes. Bodies of water (lakes,
oceans, etc.) exhibit zonation associated with changes in water depth.
III.
Ecological succession is a change in community structure over time following a
disturbance.
A. Primary succession begins on bare sites that lack living organisms.
example: volcanic eruption destroys a community, creating an abiotic region.
Pioneer species (algae, lichen, plants) move in. Their presence slowly alters the
region, making it more suitable for other kinds of organisms, and they in turn alter it
by their presence and activities, making it more suitable for other kinds of
organisms, etc.
B. Secondary succession begins on sites where a disturbance destroys many but not
all members of a community.
example: forest fire kills many understory plants and consumes forest floor litter
(dead leaves and fallen branches, etc.), but older taller trees of some species (those
that are fire-adapted) survive. If the fire is not too hot, soil organisms will also
survive.
IV.
The 3 types of changes described above emerge from a variety of community and
ecosystem interactions.
A. Abiotic factors determine plant distribution.
examples: algae: nutrients, light, pH, salinity, temperature
Grass: nutrients, moisture, drainage, organic content, pH, temperature
B. Biotic factors are linked to abiotic factors by energy flow as organisms eat one
another (trophic interactions)
1. food chains and food webs describe how energy moves through a
community.
2. the organisms in a community can be divided into trophic levels based
on the ways in which they obtain their energy.
Producers (plants, algae, phytoplankton) photosynthesize (convert solar energy to chemical
energy stored in living tissues).
Consumers obtain energy by eating producers or other consumers.
- herbivores eat producers.
- Carnivores eat other consumers.
- Omnivores eat both producers and consumers.
- Scavengers and decomposers eat bodies of dead organisms or their waste products.
In a food chain or food web diagram, arrows point to the organism doing the eating (in the
direction of energy flow).

Algae 
snail

fish

turtle
Grass 
grasshopper

songbird

hawk
[more on these in Unit 2]
C. Although trophic interactions explain much about community and ecosystem
structure, organisms rely on one another and their environment in other ways.
1. nesting substrate and materials
examples: Golden-cheeked warblers (Dendroica chrysoparia)use peeling
bark from mature ashe juniper (Juniperus ashei) trees to build nests; Cliff
Swallows (Hirundo pyrrhonota) build nests attached to cliff faces (or
similar man-made structures)
2. shelter-building materials
example: beavers require trees of a certain size and density to build dams
and lodges
D. These interspecific interactions can be strong selective factors in evolution, as
species “adapt to”* successfully cooperate with one another, compete with one
another, and/or defend themselves against one another.
1. herbivory occurs when animals eat plants. May cause damage to plant
or kill it.
2. predation involves a predator that eats prey.
3. parasitism is a type of symbiosis (living together) in which one
participant lives in or on the other (its host) and may harm but seldom
kill the host.
4. parasitoidism involves insects, such as small wasps, who lay their eggs
on living hosts. After hatching, the larvae feed on the host’s body and
eventually cause its death.
5. commensalism is a type of symbiosis (living together) in which one
participant benefits and the other remains largely unaffected.
6. mutualism is a type of symbiosis in which both participants benefit
from the association.





Example:
termite eats wood
Termite cannot digest cellulose (main component of wood)
Termite gut contains flagellates
Flagellate gut contains bacteria
Bacteria digest cellulose into molecules all can use
*remember, this phrase implies no conscious choice, but rather reflects the result of natural
selection editing out what doesn’t work in a particular community or ecosystem
V.
Summary of types of change occurring in communities as a result of organisms
interacting with one another and their physical environment.
A. Evolution occurs as the alleles present in populations change as a result of
individual organisms’ interactions with their abiotic and biotic environments.
B. Zonation occurs as abiotic factors influence the types of living organisms that
can be supported in an area.
C. Succession occurs when a disturbance disrupts community structure by killing
some species outright and/or altering their environment in ways that make it
unsuitable for their continued existence.